While we're sharing simple note taking functions, here's mine that I used for a few years. :)

    function nod { mg +-1 "/home/user/notes/$(date "+%Y-%m-%d").txt"; }

* 'nod' stands for "notes of (the) day" and was quick to type.

* 'mg' is micro emacs, my first shell-based editor thanks to OpenBSD. The '+-1' syntax means "open at end of file" so I could easily append.